Modern machinery can include one or more subsystems in their exhaust systems, for example subsystems to reduce emissions of certain materials for compliance with emissions regulations. Some of these subsystems may be more susceptible to damage from heat or other factors than other exhaust subsystems. It would be desirable to have systems in place that can help protect some of these more susceptible subsystems from factors that can reduce their effectiveness or durability.
For example, a machine exhaust system can include a diesel particulate filter (DPF), a DPF regeneration system, and a diesel exhaust fluid (DEF) dosing unit. The DPF collects soot and other particulates in the machine exhaust. During DPF regeneration, diesel fuel can be used to increase exhaust temperatures and clean the DPF. The DEF dosing unit can be used to inject urea into the exhaust stream in order to reduce NOx to meet emissions regulations. The DEF dosing unit can be installed downstream of the DPF where, during DPF regenerations, exhaust temperatures can become significantly elevated. In this scenario, during DPF regenerations, the DEF dosing unit is also exposed to these high exhaust temperatures used for cleaning the DPF. The DEF dosing unit can be cooled by both engine coolant and the urea that it is injecting while the engine is running. If the machine is shutdown during DPF regeneration, the elevated exhaust temperatures and exhaust energy can be trapped in the insulated exhaust tubing. The DEF dosing unit is then trapped in significantly high temperatures for a long period of time, which can lead to component damage and ultimately component failure. The DEF dosing unit is most susceptible to failure during this shutdown condition (engine not running), because when the engine is shutdown, the engine coolant and urea flow which usually cool the DEF dosing unit also stop. Thus, for this situation, it would be desirable to have systems in place that would delay engine shutdown to allow sufficient cooling of the DEF dosing unit.